When the United States launched the KH-9 Hexagon spy satellite into orbit atop a Titan IIID rocket in 1974, it brought with it an in-flight calibration target: the S73-7 Infrared Calibration Balloon (IRCB). This 66 cm (26 in) diameter inflatable satellite was ejected by KH-9, but failed to inflate to its intended configuration and became another piece of space junk. It was initially tracked in the 1970s, but disappeared until it briefly resurfaced in the 1990s. Now it has popped up againafter twenty-five years.
like Noticed by [Jonathan McDowell] which stumbled over S73-7 in recent debris tracking data, has very likely been tracked before, but is hidden in the noise because it is not an easy target to track. Because it is not a large metal object with a large radar cross-section, it is among the most difficult signals to reliably pick up from noise. It can also be seen in [Jonathan]’s Debris tracking tableThis is not a unique situation, as there are many missing (XO) entries. This always raises the interesting question of whether a piece of debris has diminished in orbit to where it burned up, ended up colliding with other debris/functioning satellite, or simply disappeared.
Right now, we know where S73-7 is, and as long as its orbit remains stable, we can predict where it will be, but it highlights the difficulty of tracking the roughly 20,000 objects in Earth’s orbit, with disastrous consequences if we get hold of them. it’s wrong to.
